There was a post not long ago that had a link to the "before black" GN website. It has a lot of good information on the HP ratings and the various years/drive trains. According to that source, there were no FWD GN'*, but rather there was a LaSabre that was all black and carried the Buick 6 logo--which is the orange/red 6 with an arrow integrated. This is the same logo--less the "Grand National" words that the GN used...but it is neither turbo, nor is it a GN. I believe it was a 1987 or 1988 model. It was very sharp and did have the 3.8 Buick FWD.
As for the GN'*, The years of production were '82, '84-87, and all were RWD. They also made Buick Regal T-Type'*, some of which were Turbo 3.8'*. Others were 4.1 NA and 3.8 NA. As for the HP, only the 1985-1987 GN'* had more HP than our Series II NA engines. The early Turbo 3.8 were producing around 170 HP. Of all the GN'*, the 1987 was by far the quickest, having an intercooler.
I believe that your motor mounts would be the most dificult physical barrier, along with finding a bellhousing for the tranny. But then you will get into PCM problems as well.
Even if the '84 GN is rusty and not as fast as an '85-87 GN, it is still a collectors car and can most likely be restored. This was before they were painted black, and are generally not recognized as collector cars by the uneducated...yet. This happened to the GTO in the '80'*, you could pick them up cheap. Now you can't touch one in rough shape for under 5 Grand. If you get the money, pick it up. Even if you can't do anything with it now, it will be worth your investment in the long run.
Good luck in your decision.
P.*. I am not an expert on the subject, I am only telling what I remember from past drooling and from reading the guy'* website. I believe he is knowledgeable but I have not done the research myself, and I welcome any proof to the contrary to what I have posted above. NO FLAMES PLEASE!
Retired Moderator, The Bonneville Club www.bonnevilleclub.com
RIP Oldsmobile, April 29
1995 Bonneville SE Supercharged (Stock)
Current Mods: Dirty GYM Sock air freshener.